This application is based on Patent Application No. 2000-117064 filed Apr. 18, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a print liquid tank for supplying a print liquid to a print head that prints on a printing medium, and to a printing apparatus having the print liquid tank.
2. Description of the Related Art
A continuous type large industrial printing apparatus was once a mainstream ink jet printer. An ink jet printer as a printing apparatus using an on-demand type ink jet print head came into wide use. As for an ink storage system in the ink jet print head, when a faster printing speed of the ink jet print head began to increase the ink consumption in recent years, the merits of the ink storage bag that can provide a large capacity of ink storage relatively easily ,received attention. This is because, as there are growing demands for more varied kinds of prints, from conventional monochromatic prints to color prints of symbols and characters to high vivid prints such as photographic images, the number of inks used and the amount of each ink consumed have increased dramatically. For example, a conventional monochromatic print of A4 size uses 30-60 mg of ink per sheet at most whereas a full color image print requires about 500-2000 mg/sheet.
There are many proposals concerning the ink storage system using the bag in an ink storage system, and many proposals concerning system for detecting an amount of ink remaining in the ink storage bag are open to the public.
The system for measuring the amount of ink remaining in the ink storage bag has a mechanism that visually indicates the remaining amount of ink, as disclosed for example in Japanese Patent Application Laid-open Nos. 158977/1980 and 211482/1983.
While many technologies have been proposed publicly which concern the ink storage bag and system which measure the amount of ink remaining in the ink storage bag, but, they are mostly not put to practical use or, if adopted, only for a short period of time.
Among the reasons for this are a problem of a precision at which the remaining amount of ink is detected, a problem of increased steps in the assembly process, a problem that the remaining amount of ink can only be indicated but cannot be fed back to the printer body, and a problem of requiring a generous cost increase for implementing the feedback.
Examples of the conventional systems are detailed below. In Japanese Patent Application Laid-open Nos. 45638/1972 and 21443/1976, for example, the amount of remaining ink is detected based on a change in the amount of light passing through the ink. This method detects not the actual amount of the remaining ink but only the presence or absence of the ink. That is, it has a drawback of being unable to detect a change in the ink consumption and also a drawback of requiring a mechanism for generating light and a device for detecting the amount of light transmitted and converting the detected light output into a digital value or electric signal.
Proposed methods other than the one based on the change in the amount of light that has passed through the ink include one in which an ink level displacement resulting from the consumption of ink in the ink storage bag arranged inside a case is converted by a strain-resistance gauge into a change in electric resistance (Japanese Patent Application Laid-open No. 34966/1982); one which converts the ink level displacement into a change in electrostatic capacitance (Japanese Patent Application Laid-open No. 34990/1982); one having a mechanism that visually displays the ink level displacement as above(Japanese Patent Application Laid-open No. 158977/1980, 211482/1983); and one that converts the ink level displacement into a change in the amount of reflected light or magnetism (Japanese Patent Application Laid-open No. 194855/1984, 169679/1993).
In these non-contact detection systems (based on electrostatic capacitance for example), variations in the deformations of the individual ink storage bags that may degrade the detection precision must be considered. Particularly in the systems that detect changes in the electrostatic capacitance and magnetism, these changes are inversely with the square of the distance , which is disadvantageous to the detection of the remaining mount of ink. This is because an initial change is large and a change at the last stage extremely small, making it difficult to detect a final point in the amount of remaining ink (minimum amount of remaining ink), the most critical information.
In the case of a light reflection type ink consumption detection unit, as shown in Japanese Patent Application Laid-open No. 169679/1993 and in FIGS. 14A and 14B, an ink consumption detection unit 6 is rigidly held inside a case 2 so that it faces an ink storage bag 4 (hereinafter referred to also as an ink bag) accommodated in the case 2.
The ink bag 4 is provided at one of its ends with a joint portion 8 which has a needle 10 communicating the interior of the ink bag 4 with the interior of the print head to supply the ink IN contained in the bag to the print head.
The ink consumption detection unit 6 comprises a light emitting element portion 6A, which has a light emitting diode LED or infrared LED to emit a light beam toward the surface of the ink bag 4 made from an aluminum foil composite film, and a light receiving element portion 6B that detects the light beam reflected from the surface of the ink bag 4. A signal output from the light receiving element portion 6B of the ink consumption detection unit 6 and representing an amount of reflected light corresponding to the reflectivity is an analog signal and thus requires an A/D converter to produce a signal that indicates the remaining amount of ink.
Although the ink consumption detection unit 6 is shown to be small relative to the ink bag 4 in FIGS. 14A and 14B, the size of the unit 6 is difficult to reduce. The ink consumption detection unit 6 measures e.g. about 30 mm high by 15 mm wide by 40 mm long. One of the reasons that the unit 6 has such a large size is that the ink bag 4 has a thickness or height of at least 5 mm in connection with a minimum required amount of stored ink (at least 20 ml or more) and that the unit 6 is required to have a sufficient depth of focus to cover the change in the bag height. Among other reasons result from design conditions that consider the formation of a light path between the light emitting element portion 6A and the light receiving element portion 6B, the mounting of these elements to the substrates and to the case 2 and the securing of wiring portions of the substrates. Further, the arrangement of the ink consumption detection unit 6 at the side of the ink bag 4 increases an idle space within the case 2, deteriorating the accommodation efficiency of the case 2.
When the ink bag 4 changes its state from FIG. 14A in which it is filled with a predetermined amount of ink IN to FIG. 14B in which the ink IN is consumed, the ink consumption detection unit 6 outputs a signal representing the amount of reflected light in response to a change in degree of light reflectance.
At the time, the ink bag 4 is formed of a reflective aluminum foil composite film and, because of the presence of the joint portion 8, has a sufficient rigidity not to collapse completely when the ink IN is consumed. Hence, there are some variations in the thickness of the bag. In such cases, variations in the reflection direction of the light beam in the ink consumption detection unit 6 and variations in the amount of reflected light detected by the light receiving element portion 6B may combine to make the precise detection impossible. To prevent this, a spring member that urges the ink bag 4 in the contract direction needs to be installed in the case 2. If such a spring member is provided, the ink residual amount detection of this system cannot be realized with good reproducibility without using a joint portion that can withstand the inner pressure produced by the urging force of the spring member.
In the system described above that detects a change in the reflected light amount, there is an advantage that the range of signal level change can be increased by making the signal level corresponding to the final point or its vicinity in the amount of remaining ink (near the minimum amount of remaining ink) maximum. On the other hand, however, the system requires a lens and other system of optical path to increase the focal depth corresponding to nearly the minimum amount of remaining ink. When such systems are not provided, shifts or variations in the position and angle of the surface of the ink storage bag cannot be corrected, making it impossible to reliably measure the change in the amount of remaining ink, though it may be possible to detect the presence or absence of ink.
Further, in the above detection method that converts the displacement or deformation of the ink bag resulting from ink consumption into a change in electric resistance, electrostatic capacitance, reflected light amount or magnetism, a device or circuit is required for transforming the signal obtained into a concrete electric signal. When, for example, seven color ink storage bags are mounted in the ink jet printer, seven devices or circuits need to be provided.
Here, the critical difference between the presence/absence of ink in the ink bag 4 and the amount of ink consumption (remaining amount) will be detailed. The presence/absence of ink simply means the detection of whether or not the ink exists. On the other hand the amount of ink consumption (amount of remaining ink) is taking numerical form of how much of the ink has been used or how much ink remains.
Because the ink consumption in the printer has increased as above, this difference is important. Specifically speaking, occasions often occur when a text containing photographic images (such as a catalog containing photographs) is printed by an ink jet printer for a total of, say, 100 copies. Or individual images may be printed for a total of about 20 copies to produce documents (e.g., a report in a booklet form containing photographs). If 0.1 g of cyan ink is used for one printed sheet, 100 sheets consume 10 g of cyan ink. When only 5 g of ink remains in the ink tank, the print task under consideration cannot be completed. Or in the middle of the printing process the printer outputs a printed image with no cyan ink on it. This problem can occur with the method that detects only the presence/absence of ink.
When a device capable of detecting the amount of ink used (amount of remaining ink) with a certain extent precision is adopted, the problem mentioned above can be predicted in advance. That is, when the device sends a detection signal from the printer to a personal computer or a print image output instruction system, an appropriate step can be taken.
One of the methods for preventing the above problem is to visually display the amount of remaining ink by changing an indication color. The printers are not always attended by an operator and thus when a necessary signal is to be transferred through a network or online transmission to a remote location (as by facsimile), it""s self-evident that simply displaying the amount of ink used (remaining amount) cannot cope with the event described above.
To solve this problem, a method has been proposed as shown e.g., in Japanese Patent Application Laid-open Nos. 34967/1982 and 204565/1984, in which a change in the amount of ink consumed is measured by cutting of the a conductive member disposed between the ink bag and the case with contraction of the ink bag in response to displacement or deformation of the ink bag resulting from ink consumption this method is a system which is cut off or opened when the final stage or its vicinity of ink consumption (minimum amount of remaining ink) is reached, thus making it possible to detect the amount of ink consumed or the amount of remaining ink easily and more reliably.
The ink remaining amount detection device of a type that cuts off or opens the conductive member, for example as shown in FIGS. 15A and 15B, includes: a conductive member 20 having its intermediate portion in contact with the surface of the ink bag 16 through an opening 14a of an ink tank case 14 installed in an ink tank accommodating portion 26; clips 18A and 18B connected to the ends of the conductive member 20; and a detection circuit having electrodes electrically connected to the clips 18A and 18B,respectively.
The inside of one end of the ink bag 16 communicates with an ink supply passage 26a through a stationary needle 22 and an elastic member 24. The ink bag 16 is pushed down by a press member 28 through an opening 26a provided in the ink tank accommodating portion 26.
In this construction, as the ink in the ink bag 16 is consumed, the ink bag 16 pressed by the press member 28 contracts and the intermediate portion of the conductive member 20 moves together with the surface of the ink bag 16. When the conductive member 20 is cut off, the resistance between the clips 18A and 18B becomes infinite, with the result that the detection circuit decides that the amount of ink remaining in the ink bag 16 is less than a predetermined value.
In the ink remaining amount detection system based on the circuit opening, however, a predetermined pressing force needs to be applied by the press member 28 for enhanced precision of the measurement. Variations in the pressing force from the press member 28 may undesirably cause the ink in the ink bag 16 to flow out through the stationary needle 22 and the elastic member 24 into the ink supply passage 26a. 
Further, to ensure that a change in the amount of ink consumption can be precisely measured at around the final point in the ink consumption (near the minimum amount of remaining ink), the displacement or deformation up to the final point in the ink consumption must be constant at all times. To realize this, a predetermined urging force needs to be applied to the ink bag 16.
The experiments conducted by the inventor of this invention have found that this urging force is about 98.0 Pa (reference value: 1 g/cm2) or larger when the ink bag is made from a polyethylene film 0.1 mm thicknessr and the stationary needle 22 has an outer diameter of 2 mm. When the ink bag is formed of a multilayer film of, for example, aluminum foils and silica composite films and the similar stationary needle 22 is used, the urging force is found to be about 147.0 Pa (reference value: 1.5 g/cm2) or larger based on an experiments conducted by the inventor of this invention.
The urging force depends on the surface tension of ink, the dimensions of an ink discharge port of the ink bag, and the material of the bag. When the ejection opening of the ink jet print head are around 20 xcexcm in diameter and if an ink pressure of about 245 Pa (reference value: about 2.5 g/cm2) is applied, then the ink may leak out of the ejection opening of the print head.
If the ink bag filled with ink is 1 cm or more in thickness, the ink is likely to leak. Because the ink jet print head has pressure variations, which depend on the sliding, moving and vibrating motions, the ink is supplied to the print head generally under the pressure of xe2x88x921 cm head (negative 1 cm head or more).
This requires the ink bag to be arranged at a position far below the ink jet print head in the gravity direction (more than 6 cm below). Below the print head there is generally a printing medium such as paper, which makes it impossible to install the ink bag beneath the ink jet print head.
Another possibility is placing the ink bag at a position much lower than the print head and connecting the bag to the ink jet print head through a connection pipe to supply ink to the print head.
Because the ink pressure in an ink passage running from the ink bag at its lower end to the ink jet print head at its higher end cancels the ink bag collapsing force, the urging force needs to be set that much higher. This system therefore is practically not usable. Setting the ink bag vertically erect is, of course, totally impracticable. With this method, the ink bag cannot be put at a position above the print head or at a position equal to or higher than the plane on which the print head is arranged. To solve this problem requires some provision at the discharge port of the ink bag which can withstand these pressures, prevent leakage and supply ink in a predetermined quantity.
In the method that arranges some conductive member between the ink bag and the case and determines the ink consumption or the remaining amount of ink based on a change in the gap between the ink bag and the case, this problem may be solved by adopting an ink bag construction in which an ink passage valve capable of withstanding the above-described urging force and supplying ink to the print head is integrally installed at the discharge port of the ink bag. To detect the gap change accurately, the urging force of about 98.0 Pa (reference value: 1 g/cm2) or more needs to be applied.
(1) A basic construction based on the provisions described above was manufactured. It has been found that because the ink bag is soft, the conductive member cannot be put in its place easily even by placing the rigid flat plate (e.g., iron plate) on the outer circumferential surface of the ink bag. Further, when the conductive member is made from a coiled spring or leaf spring, it is kept in a deformed state. Hence, in long-term storage or distribution tests accompanied by temperature and humidity changes, the conductive member is found unable to get cut off at a predetermined position and creep deformations cause it to get cut off before it reaches the predetermined position, which is undesirable.
It is therefore very difficult to put such a turn-off contact mechanism in place with high reliability. Automating the assembly of the mechanism and securing a long-term reliability are also difficult to achieve.
(2) In such a turn-off contact system, the output potential level changes from a high level xe2x80x9cHxe2x80x9d to a low level xe2x80x9cLxe2x80x9d. The system has a drawback that the current flows at all times until the minimum amount of remaining ink is detected (energy loss). A visual display of any kind cannot be made directly from a status change of the signal from xe2x80x9cHxe2x80x9d to xe2x80x9cLxe2x80x9d. To make some kind of visual indication requires an inversion circuit and an amplification circuit. In the turn-off contact system that changes the signal level from xe2x80x9cHxe2x80x9d to xe2x80x9cLxe2x80x9d, if the above-described conductive member is directly used to issue a warning of the residual ink amount with a light emitting diode (LED), the turn-off contact system needs to have an inversion circuit (made up of transistors) for inverting the signal and also an adjustment resistor, thus, the structure is not only complex, the structure also increases the cost of the product.
With a view to overcoming the above problems, it is an object of the present invention to provide a print liquid tank for supplying a print liquid to a print head that prints on a printing medium and a printing apparatus having the print liquid tank, wherein the print liquid tank can easily and precisely detect the amount of ink remaining in the ink tank and directly produce digital signals representing the remaining amount of ink without using a conversion element such as an A/D converter or D/A converter.
To achieve the above objective, the print liquid tank according to the present invention comprises: a storage portion made from a flexible material to be contractible or expandable, the storage portion storing a predetermined amount of print liquid and discharging the print liquid; a pressing member for pressing against the storage portion; an electrode member having an electrode portion, the electrode portion having one of its ends connected to an outer circumferential portion of the storage portion, the outer circumferential portion contracting as the print liquid is consumed, the electrode portion representing a consumption level of the print liquid; a contact electrode unit electrically connected to the electrode portion of the electrode member to issue a detection output representing the consumption level, when the contact electrode unit being moved relative to the electrode portion of the electrode member as the print liquid is consumed, the contact electrode unit detecting when a predetermined consumption level or more is consumed and issuing the detection output; and a on-off control valve provided in the storage portion to control discharging of the print liquid.
The printing apparatus having the print liquid tank according to the present invention comprises: the print liquid tank according to claim 1; a printing portion supplied with a print liquid from the print liquid tank and ejecting the print liquid to perform a print operation; and a controller to control the control valve and issue an output representing the liquid consumption in the storage portion according to the detection output from the contact electrode unit.
As can be seen from the foregoing description, the print liquid tank of this invention and the printing apparatus having the print liquid tank include: an electrode member having a plurality of electrode portions, the electrode portions having one of their ends connected to an outer circumferential portion of the storage portion, the outer circumferential portion contracting as the print liquid is consumed, the electrode portions being moved according to the liquid consumption level; and a contact electrode unit electrically connected to the electrode portions of the electrode member to issue a detection output representing the consumption level, when the contact electrode unit being moved relative to the electrode portions of the electrode member as the print liquid is consumed, the contact electrode unit detecting when a predetermined consumption level or more is consumed and issuing the detection output. Because of this construction, the amount of ink remaining in the ink tank can be detected easily and precisely and a signal representing the remaining amount of ink can be directly obtained without using a conversion element such as a converter.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.